1. Field of the Invention
The present invention is related to paper-making, and more particularly refers to the production of a high strength low cost paper having a light colored face liner surface particularly well adapted for use as cover sheets in the production of gypsum wallboard.
2. Description of the Prior Art
Paper for gypsum board is conventionally made by pulping up waste paper constituents of old corrugated paper, or kraft cuttings and waste news. In cleaning, screening and refining the suspended materials in water suspension, the processed paper stock is diluted still further with water and then formed by draining the plies of paper on several continuously moving wire cylinders, where the separate plies are joined together by a carrying felt. The weak paper web is then dewatered in a press section where water is pressed out of the web. The pressed paper is dried in a multi-cylinder drying section with steam added to each cylinder. The dried paper is subjected to a squeezing or calendaring operation for uniformity in thickness and is then finally wound into rolls. The paper is subsequently utilized as paper cover sheets to form gypsum wallboard by depositing a calcined gypsum slurry between two sheets, and permitting the gypsum to set and dry.
The present day cover sheets which are used in the production of gypsum wallboard are of two kinds. The first is used for the paper cover sheets which are used for the back side of the wallboard, and is formed of recycled wastepaper having many contaminants and a dark color. The second type is used on the outer face side of the wallboard. This is the decorated side. It is generally found as a multi-ply sheet with 2 to 7 filler plies comprised of clean waste paper furnishes such as kraft and boxboard cuttings of a hard stock nature and 1 to 2 topliner plies consisting of mainly flyleaf shavings and newspapers of a soft, groundwood quality used to provide a light, manila colored smooth appearance on the face surface of the gypsum wallboard. The flyleaf shavings waste paper grade can be described as baled trim of magazines, catalogs and similar printed and unprinted material. It contains predominantly bleached chemical fibers, but may also contain as much as 10-40 percent of clays and pigments from coating overlays.
As stated above, the 2 to 7 filler plies of the face cover sheets are comprised of clean hard stocks such as kraft and boxboard cuttings. These particular furnish constituents are of such a nature that they are inherently strong. Equally important, they can develop further strength on refining. As a result of these favorable pulp qualities, the final total sheet strength of the gypsum board face cover sheets is predominantly dependent on the furnish make-up of the cover sheet's 2 to 7 filler plies. The refined hard stock fibers comprising the filler plies are further identified with easy dewatering, fast drainage, and easy drying. This translates into faster paper production and less energy requirements for drying. In addition, the resultant sheet filler structures are very open or highly pourous. This further translates into easier gypsum board drying and faster board line speeds.
In sharp contrast, the furnish components of the 1 to 2 topliner plies which are used to provide a suitable light colored, smooth face appearance are generally formed of 70-80% flyleaf furnish, old magazine and trim, and 20% waste news. These topliner plies behave in quite a different fashion. The soft ground wood waste newspaper constituent is inherently weak in strength qualities and has minimal potential for increased strength development. In fact, it has been found that the liner plies of flyleaf furnish and groundwood newsprint provide little if any strength to the finished total sheet. The high proportions of inert clays and fillers contained in the flyleaf shavings stock constituent further substract from the integrity of the liner plies. Moreover, the soft stocks and clays contained in the manila liner overlay produce a furnish pulp historically noted for poor dewatering, slow drainage, and difficult drying. This results in slower paper production and increased energy requirement for drying. Briefly summarized, it can readily be seen that the current cellulosic furnish consisting of waste newspapers and flyleaf shavings that typically is used as topliners of the manila gypsum wallboard paper grade contributes to substantial furnish and operational problems. It provides negligible strength to the finished sheet. In addition the pulp slurry dewaters with difficulty, thereby adversely affecting the draining and drying conditions of the total filler/liner sheet. This results in poorer machine operability, lower production rates, and increased energy requirements.
Obviously, one corrective measure to obviate these problem conditions would be to replace the current "waste" stocks with "virgin" stocks. This would allow for predictable liner ply strength and would eliminate the critical clays and fillers associated with the flyleaf overlays. However, the cost of doing so would be prohibitive.
The filler plies conventionally utilized in the manufacture of paper for use in the manufacture of gypsum wallboard comprise various recycled papers. The plies have excellent strength and suitable porosity for rapid evaporation of moisture. However, they generally produce a paper which is quite dark in color and not suitable for use on the face surface of gypsum board which conventionally must have a white or manila color. Consequently, conventionally one or two liner plies are applied on the outer surface of the face paper to give the paper the required light color. The recycled paper conventionally used for the production of filler plies and which are utilized to produce the filler plies of the present invention are mixed paper, boxboard cuttings, corrugated containers, new corrugated cuttings, new double kraft lined corrugating cuttings, new kraft corrugated cuttings, used brown kraft bags, mixed kraft bags, sorted brown kraft, new brown kraft cuttings, new brown kraft bag waste, and new brown kraft envelope cuttings.
Liner plies are conventionally made from news, super news, special news de-ink quality, over-issue news, mixed shavings, groundwood shavings, white newsblanks, flyleaf shavings, manila tabulating cards, computer printout, and coated groundwood sections.
Following are definitions of the various recycled paper pulps listed above, as defined in Paper Stock Institute of America, Paper Stock Standards and Practices, Circular PS-77.
Mixed paper consists of a mixture of various qualities of paper not limited as to type of packing or fibre content.
Boxboard cuttings consists of baled new cuttings of paperboard such as are used in the manufacture of folding paper cartons, set-up boxes and similar boxboard products.
Corrugated containers consists of baled corrugated containers having liners of either jute or kraft.
New corrugated cuttings consists of baled corrugated cuttings having two or more liners of either jute or kraft. Non-soluble adhesives, butt rolls, slabbed or hogged medium, and treated medium or liners are not acceptable in this grade.
New double kraft lined corrugated cuttings consists of baled corrugated cuttings having all liners of kraft. Non-soluble adhesives, butt rolls, slabbed or hogged medium, and treated medium or liners are not acceptable in this grade.
New kraft corrugated cuttings consists of baled corrugated cuttings having all liners of kraft. The corrugated medium must be either semichemical or other similar uniform medium, Non-soluble adhesives, butt rolls, slabbed or hogged medium, and treated medium or liners are not acceptable in this grade.
Used brown kraft bags consists of baled brown kraft bags free of objectionable liners or contents.
Mixed kraft bags consists of baled used kraft bags free from twisted or woven stock and other similar objectionable materials.
Sorted brown kraft consists of baled clean sorted brown kraft papers, free from twisted or woven stock, sewed edges and heavy printing.
New brown kraft cuttings consists of baled new unprinted brown kraft cuttings or sheets entirely free from sewed edges, twisted or woven stock.
New brown kraft bag waste consists of new brown kraft cuttings and sheets, including misprint bags. Stitched or sewed papers are not acceptable in this grade, and
New brown kraft envelope cuttings consists of baled new unprinted brown kraft envelope cuttings or sheets.
The definitions of materials utilized for liner plies taken from the same publication are as follows:
News consists of baled newspapers containing less than 5% of other papers.
Super news consists of baled sorted fresh newspapers, not sunburned, free from papers other than news, containing not more than the normal percentage of rotogravure and colored sections.
Special news de-ink quality consists of baled sorted fresh dry newspapers, not sunburned, free from magazines, white blank, pressroom over-issues, and paper other than news, containing not more than the normal percentage of rotogravure and colored sections. This packing must be free from tare.
Over-issue news consists of unused over-run regular newspapers printed on newsprint, baled or securely tied in bundles, containing not more than the normal percentage of rotogravure and colored sections.
Mixed shavings consists of baled trim of magazines, catalogs and similar printed matter, not limited with respect to groundwood or coated stock, and may contain the bleed of cover and insert stock as well as beater-dyed papers and solid color printing.
Groundwood shavings consists of baled trim of magazines, catalogs and similar printed matter free from beater-dyed papers, and may contain not over 5% of solid color printing.
White newsblanks consists of baled unprinted cuttings and sheets of white newsprint paper or other papers of white groundwood quality, free of coated stock.
Flyleaf shavings consists of baled trim of magazines, catalogs and similar printed matter. It may contain the bleed of cover and insert stock to a maximum of 10% of dark colors, and must be made from predominately bleached chemical fibre. Beater-dyed papers may not exceed 2%. Shavings of novel news or newsprint grades may not be included in this packing.
Manila tabulating cards consists of printed manila-colored cards, predominately sulphite or sulphate, which have been manufactured for use in tabulating machines. This grade may contain manila-colored
Computer printout consists of white sulphite of sulphate papers in forms manufactured for use in data processing machines. This grade may contain color stripes and/or computer printing, and may contain not more than 5% of groundwood in the packing. All stock must be untreated and uncoated, and
Coated groundwood sections consists of new printed, coated groundwood papers in sheets, sections, shavings or guillotined books. This grade shall not include news quality groundwood papers.